In recent years, a two-beam angular multiplexing technique has been proposed as hologram technology capable of recording and reproducing a large volume of data at high speeds. This technique faces a challenge to controlling a relative angle of beams of signal light and reference light.
For this challenge, Patent Literature 1 discloses therein a scheme to control the relative angle of a reference beam with respect to a signal beam by detecting the signal beam by an image-sensing element in order to search the relative angle of a signal beam and a reference beam, computing per recording angle a signal-to-noise ratio (SNR) which is reproducing performance, and predicting the next relative angle from such value.